The present invention relates to a bench top scale device for testing the potential of compression ignition engine fuel compositions which form deposits on engine components during engine operation; and a method for testing said fuel compositions that yields data measuring the propensity of said fuel compositions to form deposits that negatively effect engine operation; said data correlating directly with results obtained in testing said fuel compositions in engines operating under in use conditions.
During operation the hot surfaces within an internal combustion engine are exposed to many fluids, both liquid and gaseous, which may undergo thermal breakdown resulting in the formation of deposits on the surfaces of these components, thus compromising engine function. Examples of the fluids which an engine component might be exposed to are fuel compositions, lubricating fluids, and combustion byproducts. Those skilled in the art are aware of the methods and apparatus generally employed for screening fuel compositions for their tendency to form deposits that can compromise engine functionality. Because of the limited ability of bench top scale apparatus and methods to duplicate the conditions encountered in an operating engine, ultimately fuel compositions are tested in a running engine, under simulated xe2x80x9creal worldxe2x80x9d operating conditions to determine how well these fuel compositions perform in terms of suppressing the formation of engine deposits or removing engine deposits once formed. Such tests are expensive, and because of the cost of the equipment and the duration of the test, the use of test engines to determine fuel and other fluid performance is prohibitively costly to do a broadly based xe2x80x9cscreeningxe2x80x9d type of study.
Traditionally, bench top scale testing equipment and methods utilized to xe2x80x9cscreenxe2x80x9d fuel compositions for their propensity to form disadvantageous deposits have been based on the notion that simple thermal degradation of fuel compositions can be correlated to the performance of these fuel compositions when they contact xe2x80x9creal worldxe2x80x9d components in xe2x80x9creal worldxe2x80x9d engines operating under xe2x80x9creal worldxe2x80x9d conditions. For this reason, most of the apparatus utilized in such screening tests employ some scheme in which fluids or vapors of the fuel composition are contacted with a substrate and then heated, generally under steady state conditions. However, it is well known in the art that simple static heating of a fuel composition and observation of the amount of deposits thereby formed correlates poorly, if at all, with performance of such fuel compositions in engines operating under real world or simulated real world conditions. Those skilled in the art understand that many factors in addition to thermal conditions within the engine environment influence the formation of engine deposits. These factors include the nature of the fuel composition, the type of material from which an engine part is made and its surface finish, the thermal history of the surface during its exposure to the fuel composition, and the presence of other fluids (such as coolant, engine exhaust, or lubricant vapors) admixed with the fuel composition during contact with the engine part""s surface. Additionally construction features of the engine components such as fine passageways, orifices, or sharp edges can also contribute significantly to variations in the rate of deposit formation and its impact on engine functionality.
To illustrate this point, an example from the prior art of fuel testing apparatus may be cited. In U.S. Pat. No. 3,059,467 to Meguerian et. al. an apparatus is described in which a metered continuous flow of liquid fuel is passed along an inclined heated conduit along with a stream of air, the heated region being either of uniform temperature or a gradient temperature over the length of the conduit, and the heating being either steady state or increasing throughout the determination. After a period of time during which fuel and air are passed through the apparatus, the conduit is removed from the apparatus and weighed, the weight being compared to its weight prior to exposure to the fuel composition to determine the amount of deposits left by decomposition of the fuel. The results obtained using this method were compared with results of two different xe2x80x9creal world enginexe2x80x9d tests. These data showed that for a given fuel composition and set of test conditions repeatability of the apparatus was poor. In several identical tests the apparatus yielded deposit weights wherein the highest recorded was 135% of the lowest recorded.
A series of Chevorlet ISD engine tests were run using different fuel compositions and compared with those same fuel composition run in the subject apparatus. Data derived from the engine tests showed that a fuel that failed the test deposited 334% greater weight of deposits than a fuel that passed the test. Tests conducted on those same two fuel compositions using the subject apparatus and method of Meguerian et. al. gave results wherein the failing fuel composition produced deposits only 149% heavier than those of the passing fuel composition. Comparison of the data obtained from the repeatability tests with those of the data obtained from the passing and failing fuel tests indicates that the testing method of Meguerian may not give a good indication of the propensity of a fuel composition to form deposits in situations where deposit formation is dependent upon factors other than the raw chemical propensity of a fuel composition to thermally decompose. As the deposit formation is increasingly dependent upon factors other than mean operating temperature, testing equipment based upon simple thermal decomposition of fuel compositions correlates less well with the results obtained from the same fuel composition employed in an operating engine test.
Operating conditions also contribute to variations in deposit formation within engines. For example an engine running under constant load will form deposits at a different rate than one which is subjected to cycles of acceleration and deceleration under varying load and coast conditions.
In general, for bench top scale testing equipment to mimic conditions, and thus more accurately gauge the propensity of fuel materials to form deposits which lead to impairment of engine operation, they must incorporate features which permit cycling through various temperature conditions and conditions of fuel composition loading on the surface, as well as the ability to introduce other fluids into the testing apparatus under the conditions in which they would contact a surface in an operating engine. Additionally, testing apparatus must be designed so that channels and other surface features that appear within an engine are mimicked in the testing apparatus. Finally, for any apparatus to test the propensity of a fuel composition to leave deposits within an engine, it must address the problems associated with variations in surface composition and finish of the substrate upon which deposits are left within the testing apparatus, as well as provide a means of reproducibly providing a substrate surface of accurately measured surface area and finish, one of the keys to reproducible test results. Presently, this factor is either largely ignored, or is addressed through the requirement of requiring an expensively custom machined and finished substrate, resulting in elevated costs associated with testing apparatus. Due to the expense of such substrates, practitioners typically resort to cleaning the substrate after use, which preclude preservation of samples and often leaves the quality of the resulting surface finish in doubt from the perspective of a reproducible surface.
Accuracy of devices employing gravimetric measurement of deposits left on a substrate surface also suffers when low surface area substrates are employed from the standpoint that minimal catalytic surface/volume of fuel leads to small amounts of deposits being formed (thus the range of weight change in the substrate for various fuel compositions is small), and the surface area to weight ratio is low, making it difficult to accurately measure the weight change.
Additional factors, such as non-uniform distribution of fuel compositions within the test apparatus, and fuel puddling within the test apparatus can also effect the reproducibility of test data.
Operating conditions are of utmost importance when testing fuel compositions intended to be burned in diesel engines. This is particularly true when concerned with the tendency of diesel fuel compositions to leave deposits within fuel injectors. Unlike spark ignition engines, compression ignition engines have fuel delivery components exposed to combustion chamber temperatures, and during operation under xe2x80x9cmotoringxe2x80x9d conditions (engine operating under coasting or braking conditions), very high temperature gas is forced into the injectors, resulting in degradation of fuel residue left in the injector. For this reason, an apparatus used to examine the tendency of diesel fuel compositions to degrade and leave deposits must permit tests to be conducted at temperatures near the flash point of the fuel composition. This requires testing equipment that is designed to address the safety issues associated with such high temperature testing. Additionally, automating the testing equipment affords the ability to conduct tests in which the conditions within the testing apparatus are cyclic rather than static, giving a testing regime which more nearly matches the environment found in an operating engine.
U.S. Pat. No. 5,693,874 to De La Cruz discloses a test apparatus designed to simulate the conditions of the intake manifold in a gasoline engine employing port fuel injection, and the attendant conditions in which an intake valve in such a gasoline engine operates. The design is unsuitable to testing diesel fuels because of the low surface area to weight ratio of the test specimen and the absence of safety devices that would permit high temperature soak cycles.
U.S. Pat. No. 3,438,248 to Taylor et. al. discloses a device wherein the thermal decomposition of bulk fuel flow over metallic test strips may be examined. Taylor is directed at studying the conditions most commonly found in nearly empty fuel tanks of aircraft traveling at supersonic speeds. This device does not closely approximate the conditions found in an operating diesel engine and does not incorporate safety features necessary to conduct such tests at temperatures which approach the conditions found in an operating diesel engine.
U.S. Pat. No. 3,318,667 to Fabuss et. al. discloses a device designed to duplicate the results of the ASTM-CRC fuel coker test apparatus while using a drastically lower volume of fuel material in the test. Fabuss is directed at studying the thermal decomposition of fuel compositions under conditions of bulk liquid fuel flow such as would be found in the systems supplying fuel to the engines of high performance aircraft. It is not suited to studying decomposition of residue under conditions simulating those in the combustion chamber of an operating diesel engine because it relies on liquid fuel flowing through the apparatus to perform the test. This also precludes testing under conditions in which the test surfaces are exposed to gases and vapors having the chemical characteristics of other fluids such as lubricant or exhaust gas during the test.
U.S. Pat. No. 3,059,467 to Meguerian et. al. discloses an apparatus in which liquid fuel is passed along a heated conduit, the conduit being subjected to gravimetric analysis before and after exposure to the fuel. The conduit has a low surface area to mass ratio which can negatively effect the sensitivity of test data to the propensity of a fuel to form engine deposits. As with other such apparatus used to study the thermal degradation of liquid fuel streams, this device is also unsuited to simulating the conditions to which components in the combustion chamber of a diesel engine are exposed.
The present invention provides a method in which a highly reproducible low cost surface mimicks the structural morphology typically found within engines. Additionally it provides an apparatus in which the operating extremes typically found in operating diesel engines may be duplicated while maintaining a safe working environment. Additionally it provides a method of automatically determining the propensity of diesel fuel materials to form deposits within diesel engines that has good correlation with tests performed in running diesel engines.
One aspect of the present invention is to provide a bench scale apparatus in which diesel fuel compositions may be examined for their propensity to leave deposits in diesel engines under operating conditions.
Another aspect of the present invention is to provide a method of using the apparatus to test the propensity of diesel fuels to leave deposits in operating diesel engines.
Another aspect of the present invention is to provide a method of utilizing low cost materials in the testing apparatus that give a highly reproducible substrate upon which deposits are formed during the test.
Another aspect of the present invention is to provide a bench top scale apparatus in which diesel fuel compositions may be safely tested at the extreme operating conditions typically experienced in an operating diesel engine.
Yet another aspect of the present invention is to provide an apparatus in which testing of diesel fuel compositions is completely automated, requiring technician input only to set up the testing conditions and retrieve the substrate at the end of the test period.
An additional aspect of the present invention is to provide a method of utilizing a low cost substrate that leads to improvement in the sensitivity of gravimetric measurement of deposits formed during tests carried out to determine the propensity of a diesel fuel composition to leave deposits in a running engine, accomplished by increasing the surface area to mass ratio of the substrate employed over that conventionally used in fuel testing apparatus.
A further aspect of the present invention is to provide an apparatus in which the parameters of fuel loading and thermal excursion may be adjusted dynamically over a broad range, permitting testing to be carried out under conditions which closely mimic those experienced in an operating diesel engine.
Yet another aspect of the present invention is to provide an apparatus in which the conditions experienced within an operating diesel engine are further mimicked through the ability to entrain vapors and gasses that mimic other fluids such as lubricating oil and coolant encountered in an operating diesel engine.
An additional aspect of the present invention is to incorporate fire suppression equipment and a method of automatically actuating the fire suppression equipment during a determination carried out in the testing apparatus.
Another aspect of the present invention is to provide an apparatus and a method of using the apparatus to study the propensity of diesel fuel compositions to leave deposits deleterious to the operation of diesel engines which has a high degree of correlation between test data derived from the apparatus and the results observed in operating diesel engines.
Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in several views.